The present invention relates to an ultrasonic bloodstream diagnostic apparatus for providing a display of velocity profiles as a function of time, and more particularly to a circuit for providing a simultaneous display of velocity profiles and a display of an average blood flow velocity with greater accuracy than is currently available.
Ultrasonic Doppler shift imaging techniques have found extensive use in medical applications where it is desired to obtain a bloodstream spectrum in a B-scan mode on a real-time basis. To provide dual displays of velocity profiles and average flow velocity, ultrasonic diagnostic apparatus comprises a quadrature phase detector which detects phase quadrature Doppler shifted signals. These signals are digitized and fed to a digital frequency analyzer to obtain real and imaginary components of frequency spectrum. To determine the direction of blood flow the frequency spectrum data are passed through a squaring circuit and a summing amplifier to obtain power spectrum data. The power spectrum data are then fed to a logarithmic processor to reduce the number of data bits representing the power spectrum so it conforms with the B-scan monitor dynamic range with due regard to the size and cost of a scan converter and a digital-to-analog converter which processes the power spectrum data into a form suitable for display. Recently developed techniques employ microprocessors for computing the power spectrum average frequency from the compressed power spectrum data and for displaying a bloodstream average flow velocity simultaneously with velocity profiles. However, the logarithmic compression of data bits results in an average frequency value which is inaccurate due to the nonlinearity of the logarithm.